The incidence of tuberculosis in Norway in recent years has been low, but not decreasing. Tuberculosis occurs mainly among defined risk groups and there is little ongoing transmission. New regulations on tuberculosis control were implemented in 2003 based on the current national and global tuberculosis situation. Tuberculosis coordinators are appointed in each county and direct observed therapy is mandatory for all patients. Public health interventions in Norway should be targeted towards risk groups.

Background

A century ago Norway was suffering from a very high burden of tuberculosis. Norway is now one the countries in Western Europe with the lowest incidence of tuberculosis, reporting 5.7 cases per 100,000 population in 2002 (1). Tuberculosis in Norway now occurs mostly among defined risk groups. The objective of this study is to describe recent trends in notification and treatment outcome of tuberculosis in Norway and public health interventions.

Material and Methods

This article is based on data from the Norwegian tuberculosis register. Notification of tuberculosis is mandated by the Communicable Disease Act. Laboratories report findings of acid fast bacilli and positive cultures, including drug susceptibility. Clinicians report confirmed and suspected cases of tuberculosis and individual treatment outcome. All cases are notified with full identity by both laboratories and clinicians. For cases only reported from one source, reminders are sent to complete the notification. If no laboratory result can confirm the case, the clinician will be the source. The national reference laboratory at NIPH has since 1994 performed fingerprint analysis (RFLP) on all culture confirmed cases. Positive cultures are sent to NIPH for quality assurance and RFLP from 14 laboratories performing culture for M. tuberculosis in Norway. The prescription of tuberculosis drugs which are distributed from one central pharmacy, are compared with the Norwegian tuberculosis register. Contact investigations are reported by the municipal health care system.

Results

Two hundred and fifty six cases of tuberculosis were reported in Norway in 2002 (1). This included 208 new cases and 48 recurrent cases (28 with previous tuberculosis diagnosis without treatment and 20 previously treated cases). Of the 256 patients, 195 patients (76%) were born outside Norway, mainly in countries with a high burden of tuberculosis. One hundred and two of the foreign-born patients were born in Africa and 63 in Asia. Pulmonary tuberculosis was diagnosed in 61% of all cases (Figure 1).

Tuberculosis among foreign-born occurs in younger age groups (figur 2). Among Norwegian born patients 64% were male and the median age was 74 years. Median age for foreign-born patients was 29 years. 52% of reported cases among foreign-born were male, but there was a higher rate of females in the youngest and oldest age groups.

Figure 2. Notified cases of tuberculosis in Norway in 2002 by age, gender, and origin of birth

Seventy six percent of all the tuberculosis cases and 77% of the pulmonary cases were confirmed by culture. Drug susceptibility tests were performed on all (192) culture confirmed strains. Few Norwegian born patients had drug-resistant strains. Out of 42 isolates in this group in 2002, only one was resistant to isoniazid and none were multidrug-resistant (MDR-TB) i.e. resistant to both isoniazid and rifampicin. Drug susceptibility tests were performed on 150 isolates from foreign-born patients. Twenty-one isolates showed resistance to isoniazid (11%) and seven of these were also resistant to rifampicin. This is the highest number of MDR-TB cases ever reported in Norway, representing 3% of all culture confirmed tuberculosis cases. MDR-TB occurred among patients from Africa, Asia and Russia.

Eighty four percent of all tuberculosis patients notified in 2001 were successfully treated. Foreign-born patients had a higher success rate (86%) than Norwegian born patients (77%). Seven percent of the patients died during treatment and 3% defaulted. Of patients with pulmonary disease confirmed by culture, 84% were successfully treated. Among these patients, 32% completed treatment without conversion as confirmed by culture.

Discussion

Tuberculosis notification is considered to be very representative of the actual number of cases in Norway due to multiple sources of notification. The transmission of tuberculosis in Norway has been very low for many years. The incidence rate of tuberculosis among the Norwegian born population has steadily decreased. Cases occur mainly among elderly people and are primarily caused by the reactivation of endogenous foci of infection acquired earlier in life, prior to the availability of tuberculostatic drugs. Due to increased immigration, the number of reported cases in the foreign-born population has risen since the late 1980s. This explains why the overall incidence rate has not declined in recent years (figure 1). Based on RFLP results, most foreign-born patients are believed to develop disease from infection acquired in their country of origin prior to arrival in Norway (6). Among groups of foreign-born patients the tuberculosis incidence rate is comparable to the rate in their countries of origin (2).

Despite a rise in 2002, MDR-TB is rare in Norway. However, increased vigilance is needed to ensure the prevention of new MDR-TB cases by early diagnosis and effective treatment of all tuberculosis patients. Norway experienced the largest outbreak of MDR-TB ever confirmed by RFLP in Europe. One African born patient who was diagnosed in 1994 with polyresistant tuberculosis (resistant to more than one drug but not to both isoniazid and rifampicin) later developed MDR-TB due to poor management. According to RLFP analysis this case was the source of 22 secondary cases by June 2003. Nine of these cases had polyresistant strains and 13 had multidrug-resistant strains (3).

High age contributes to a higher death rate (22%) among Norwegian born patients. The short treatment period before death and diagnosis post mortem leads us to believe that Norwegian born patients suffer from delay in diagnosis, due to lack of awareness among healthcare workers. Among the foreign-born patients migration (voluntary or by deportation) was the main reason for not completing treatment. All the defaulters (3%) were foreign-born.

New regulations on tuberculosis control and guidelines on prevention and control of tuberculosis were implemented in 2003 (4,5). These regulations comply with the direct observed therapy strategy (DOTS) (http://www.who.int/gtb/dots/index.htm) promoted by the World Health Organization and the International Union Against Tuberculosis and Lung Diseases (IUATLD; http://www.iuatld.org). The guidelines emphasize early diagnosis, correct drug combination and a close follow up of patients during treatment.

The current recommendation for chemotherapy is two months of intensive phase therapy with isoniazid, rifampicin, pyrazinamid and ethambutol, followed by a four-month regimen with isoniazid and rifampicin. Ethambutol may be terminated if susceptibility results are available prior to the completion of the intensive phase and the strain is known to be susceptible to all drugs, or may be left out for older Norwegian born patients with no risk factor for recent transmission or previous treatment. Second line drugs are available for patients diseased with resistant strains.

DOTS is obligatory for all tuberculosis patients throughout the full treatment period. According to new Norwegian regulations, tuberculosis coordinators are appointed at the county level to strengthen tuberculosis control and ensure implementation of the regulations. In a country with a low incidence of tuberculosis it is a challenge to maintain a high awareness and knowledge of the disease among healthcare workers. Tuberculosis coordinators will be responsible for this important challenge.

Other interventions are screening for tuberculosis in high-risk groups including close contacts to infectious cases, drug abusers and homeless persons and immigrants from high prevalence countries. Great emphasis is put on contact tracing around infectious cases. In Norway, contact tracing only detects one new tuberculosis case for every ten index cases (5). Immigrants from countries with a high burden of tuberculosis are subjected to mandatory screening for tuberculosis when entering Norway. This includes a tuberculin skin test for all and a chest x-ray for persons over the age of 15 years. The new regulations recommend wider use of treatment for latent infection.

BCG vaccination was introduced in Norway in 1947 and was for many years a compulsory vaccine given at the age of 14. Since 1995, BCG vaccination has been voluntary. The vaccination coverage has remained high, estimated at 99% in 2001. Children in immigrant families are offered BCG vaccine at birth or when they arrive in Norway.

Public health interventions in Norway are targeted towards defined risk groups for tuberculosis. It is also very important to ensure that the health care system is accessible for persons at risk. Even with a favorable tuberculosis situation we have seen that outbreaks may occur. This reminds us that early diagnosis and close follow up of every patient during treatment is of great importance. Tuberculosis is a major global health concern and the fight against tuberculosis has to be a unified global effort. International collaboration is crucial.